This invention pertains to the art of valves and more particularly to metering valves.
The invention is particularly applicable to a new and improved soft seat assembly for a metering valve and will be described with particular reference thereto. However, it will be appreciated that the invention has broader implications and may be advantageously employed in other valve environments and applications.
Previous metering valve arrangements, have typically provided sealing engagement between the lower end of a valve stem and a metallic valve seat defined on a generally planar surface of a valve chamber. Although the durable metal to metal contact between the stem and seat provides adequate sealing for many applications, the seat or an abutment area on the valve stem is eventually subject to wear and degradation with continued use over time. Irregularities that develop between the mating metal surfaces of the stem and seat inhibit precise sealing efforts.
More recent developments have attempted to employ a soft seat that is designed for mating, sealing contact with the valve stem. U.S. Pat. No. 3,228,655 to Weise issued Jan. 11, 1966 is representative of one type of valve assembly incorporating a soft seat. The Weise patent particularly teaches a two-piece structure defining a substitute seat surface comprising, alternatively, a soft seat or hard seat. The substitute seat is suitable for modifying an original valve assembly in which a metal seat surface has become pitted and worn. Further, the substitute seat is received in the valve assembly without having to change or modify any of the remaining valve components.
The substitute seat in the above-noted patent necessarily requires a two-piece construction which is subject to further problems. Multi-part components require separate manufacture, tolerance specifications, inventory, and, additionally, are prone to deleterious wear between the cooperating members. Moreover, any movement of the substitute seat either during assembly or use, has an adverse effect on the metering function and resultant flow through the valve.
The present invention contemplates a new and improved seat assembly which allows all of the benefits of the prior construction to be realized while eliminating the above-referred to problems and others.